Date of Award
2025
Document Type
Dissertation
Degree Name
Doctor of Philosophy (PhD)
Department
Chemistry
First Advisor
Christopher C. Landry
Second Advisor
Matthew White
Abstract
Tungsten oxide (WO3) is a transition metal oxide semiconductor that has remarkable intrinsic properties that make it a suitable candidate for visible light active photocatalysis, particularly in catalyzing heterogeneous reactions. WO3 was synthesized using a hard templating approach to create a porous structure, effectively enhancing its surface area and amplifying active catalytic sites' availability. This dissertation investigates the photocatalytic reactivity of nanocrystalline porous WO3 in the degradation of small organic molecules, with a particular focus on the influence of incorporated metallic gold (Au) and platinum (Pt) nanoparticles (NPs) on reactivity and product selectivity.
Effective catalysts are vital for controlling product formation in chemical reactions, particularly for environmentally friendly C1 chemical processes. The potential of porous WO3 photocatalysts, modified with Au NPs, was investigated for the visible-light-driven oxidation of gas-phase methanol. Experiments were conducted in a continuous-flow reactor, where different parameters, including oxygen concentrations and surface methanol concentrations, were shown to influence the catalytic activity of WO3. The incorporation of Au NPs improved the reducibility of WO3, influencing its ability to catalyze reactions under light. Porous WO3 demonstrated superior methanol adsorption compared to dense WO3. Under light irradiation, this characteristic contributed to a selectivity towards dimethyl ether (DME). Adding Au NPs resulted in a shift of this selectivity towards partially oxidized products, such as methyl formate (MF), particularly with higher Au content.
The formation of acetaldehyde from bio-ethanol is crucial for synthesizing various industrial chemicals. The potential of porous WO3 photocatalysts modified with Au or Pt NPs for visible-light-driven ethanol oxidation was studied. Initial catalytic activity was noted under ambient conditions, but deactivation occurred due to adsorbed byproducts and incomplete lattice oxygen replenishment. Electron paramagnetic resonance (EPR) revealed that WO3 was reduced, leading to incomplete reoxidation and catalytic deactivation. Higher oxygen concentrations increased selectivity toward acetaldehyde (> 50%) for most catalysts, except 3 wt% Pt-WO3, facilitating complete ethanol mineralization to CO2. Increased Pt loading led to lower selective oxidation of ethanol as CO2 production rose. Additionally, water vapor reduced ethanol conversion and shifted selectivity towards partial oxidation products.
Finally, the liquid-phase oxidation of 2-chloroethyl ethylsulfide (CEES), a structural analogue of mustard gas, was investigated using porous WO3, modified with Au and Pt NPs. This process was driven by visible light in the presence of various aldehydes and molecular O2. The investigation focused on determining the optimal concentration of different aldehydes, revealing pentanal as the most effective co-catalyst for facilitating controlled oxidation. This reaction predominantly yielded 2-chloroethyl ethylsulfoxide (CEESO) with remarkable selectivity. Notably, 1 wt% Pt-WO3 exhibited exceptional activity, achieving nearly 100% conversion of CEES to CEESO while minimizing the generation of more hazardous 2-chloroethyl ethylsulfone (CEESO2)
Language
en
Number of Pages
168 p.
Recommended Citation
Tracy Jr., Robert B., "Tungsten Oxide Nanoparticles as Visible Light Photocatalysts in the Oxidation of Small Molecules: Fine Tuning Electronic Properties with Metallic Gold and Platinum" (2025). Graduate College Dissertations and Theses. 2041.
https://scholarworks.uvm.edu/graddis/2041
